6890N too slow warming up and cooling down

[seamoro]

We are running on two 6890N GC-FID are they are slow heating up and slow cooling down in comparision to our 7890 GC-FID. Is there anyway we can improve this?

[dblux_]

We are running on two 6890N GC-FID are they are slow heating up and slow cooling down in comparision to our 7890 GC-FID. Is there anyway we can improve this?

Invest in fast oven insert (P/N G2646-90400) if you meant slow oven cycles.

[Yama001]

The 7890s have altered the oven design a tad - I believe the fan will speed up at low temperatures to improve the cooling rate.

Aiming a fan at the 6890 oven flap ( the lower one) can help out if ambient temp is high, or if the GCs are set back to back.

A lot of our folks still use oven exhaust diverters that were made for the 5890s - these will redirect warm outlet air back into the oven if you are not careful - if you still have any of those you may as well toss them.

I believe the fast oven part dblux mentioned is simply a block that cuts the oven space in half, reducing the thermal mass.

[larkl]

I doubt you're ever going to get the 6890 to cool like the 7890. Agilent really improved this part of the GC. As indicated by others, a fan aimed at the back will help. Make sure the GC has a lot of open area in back and is not shoved against the wall. We find the the diverters that send the hot exhausted air upwards are quite helpful. Finally you can turn the ambient temperature in the room down a bit. You may laugh, but we have two GCs in a operating unit (non-lab personnel) and they'll call and say they're both "down". What we find is the room heat is at nearly 80 and the GCs just can't get to the starting temperature in a reasonable period of time.

[Consumer Products Guy]

Set the GC oven to a higher temperature than it is now and reach around back and feel if any hot air is coming out.

We've had this happen on a few of ours as they aged. Two needed oven flap motors to be replaced (by us), and one actually had the round flap fall off (we riveted the old one back on).

[Johnny Rod]

We have a 6890 and 7890 both running the same method, where it cools from 150C final temp to 30C. The lab is thermostatted at 21C (ish). The 6890 takes 8mins to cool (4mins to 40C, another 4 mins to reach 30C), the 7890 takes about 5 mins to cool 150 to 30, and sounds like a plane taking off. Definitely not the same oven, and this is one reason we got the 7890.

If it's crucial then you could use a cryo kit as this brings the 6890 cooling time down to about 4mins instead of 8, but it's more cost. The measures above are good though. Do check the flapper is working, I've seen them seize in the past, part open.

Finally one heating rates, if you have a 220V 6890 then it should heat at 50C/min or more. I haven't really had a go with the 7890 to see how fast it goes, what are you trying to achieve though? The 7890 seems to be quicker with everything, even inlets cooling down. Nice to see there has indeed been some progress, though much of the time it might not make any difference to the user!

[seamoro]

Bascially when are trying to reduce to total run time for a sample. Our 7890 total run time is 29mins in comparison to our two 6890s which have a total run time of 36 and 40mins. so obviously we want to reduce the prerun and post run cooling and warming on the 6890s. i think the oven insert is a pretty good idea and i gonna try that. trying to find the cryo kit option on the net now

[Johnny Rod]

Other things to consider for reducing cycle time, aside from oven performance, relate to the chromatography. If you have a surfeit of resolution then you could reduce the column length, increase carrier flow (above the optimum values), increase initial temp and/or temp ramps. We all like to see peaks with masses of separation but in reality you might need more sample turnover than glacial valley floors between peaks of interest.

[Peter Apps]

In addition to Johnny Rod's advice.

Switching from helium to hydrogen carrier gas will halve separation times. Narrower shorter columns reduce separation times. Thinner films allow elution at lower temperatures, so the heat-cool cycles are shorter. So many solutions ........

Peter

[seamoro]

more good advice thanks. But will i lose sensitivity by switching to hydrogen?

[chromatographer1]

"But will i lose sensitivity by switching to hydrogen?"

Only if by changing to hydrogen you enrich the flame's air/fuel ratio.

If you are using 0.32mm ID columns or less in ID you should not have any detectable change in sensitivity.

Of course your peaks in half the time will be almost twice as tall as they will be about one-half as wide.

Only if your analytes react with H2 at the temperatures in which you operate your instrument should there be any problem with a FID sensitivity.

best wishes,

Rod

[Peter Apps]

more good advice thanks. But will i lose sensitivity by switching to hydrogen?

Exactly the opposite, all else being equal; because the peaks are narrower with hydrogen they are higher and therefore more detectable.

Peter